The present invention relates to improvements in a dry etching apparatus which is used in processes for manufacturing a semiconductor integrated circuit etc.
Dry etching methods for use in the manufacturing processes of a semiconductor integrated circuit etc. include a plasma etching method, a reactive sputtering etching method, etc. which are extensively applied at present. In these etching methods, a reactive gas is discharged under a reduced pressure to generate reactive species such as radicals or ions, which are reacted with the surface of a substrate for etching, thereby to perform the etching. Since such dry etching is superior to the wet chemical etching in the critical dimension controllability, it has become an increasingly important technique under the circumstances under which pattern dimensions have become smaller and smaller feature sizes to necessitate patterning at the level of 1 .mu.m. Since, however, the plasma etching method or the reactive sputtering etching method sets the substrate to-be-etched in a discharge cell, it involves such problems that the damage of the substrate to-be-etched is prone to occur due to charged particles and that a resist is depleted by the radiant heat of a plasma, etc. Any countermeasure has therefore been desired.
In the processes of the plasma etching method and reactive sputtering etching method mentioned above, desired patterns of microelectronic circuits are formed via a large number of steps such as resist coating, pattern exposure, development, etching and resist peeling. Techniques for forming patterns with such complicated steps curtailed sharply have been known, and the details are described in, e.g., `Proceedings of 1983 Dry Process Symposium`, page 97 (1983), and `Electronics` (Ohm Publishing Co., Ltd., Tokyo), February 1984, page 5.
These known techniques exploit the phenomenon that, when a p.sup.+ -type silicon or undoped silicon substrate set in a reaction chamber, in which a gas containing chlorine is introduced, is irradiated with light having a wavelength of approximately 300 nm (the light of an Hg-Xe lamp or an XeCl excimer laser), only a part struck by the light is etched. Although the mechanism of this phenomenon is not sufficiently grapsed, it is interpreted as follows. A chlorine molecule absorbs the light of the wavelength of approximately 300 nm thereby to dissociate into radicals, while an electron created in the surface of the silicon substrate by photo-excitation is adsorbed to the chlorine atom to produce Cl.sup.-, which penetrates into a positively charged silicon lattice, and the silicon crystal has its bonding dissociated and vaporizes in the form of SiCl.sub.x, with the result that the etching takes place.
Owing to the technique, it is possible to sharply curtail the manufacturing steps of a large-scale integrated circuit. For efficiently photo-dissociating the chlorine gas and for raising the etching rate of the substrate, a light source which radiates high-intensity light at or near 300 nm is indispensable, and the excimer laser of XeCl or the like is deemed effective. The excimer laser, however, has the problems that it is expensive, that the power lowers gradually with operation, and that the laser gas must be periodically changed.
Another known example close to the present invention is the technique of maskless etching based on laser irradiation. In case of employing a laser as a light source, the merits of the laser; excellent directionality and focalizability can be exploited, and a microscopic etching pattern can be depicted directly without the intervention of a mask in such a way that the surface of a substrate to be etched is scanned by a fined laser beam. There is an example wherein a microscopic etching pattern was depicted on single-crystal and polycrystalline silicon by utilizing chlorine or hydrogen chloride as a reactive gas and an Ar.sup.+ laser as means for activating the gas. The details are described in `Appl. Phys. Lett.`, 38(12), 1018 (1981).
According to the paper, since the wavelength of light radiated from the Ar.sup.+ laser is separate from the center (330 nm) of the absorption spectrum of the chlorine gas, laser irradiation at high power (about 7 W) is required for efficient etching. Regarding the hydrogen chloride whose absorption band is entirely separate from the wavelength of the Ar.sup.+ laser light, a remarkable etching effect was observed for the first time when the Ar.sup.+ laser was operated at a power higher than 4 W. It is described that the etching is promoted by projecting the laser light of such high power and heating the substrate nearly into a melted state. In this manner, in the case of using the Ar.sup.+ laser in the prior art, there is the problem that expensive laser equipment capable of producing the high power is indispensable. it is also considered to replace the Ar.sup.+ laser with the excimer laser, but the excimer laser has the problems as described before and the practical use is difficult.